The present invention relates to a combination coupling and guide bearing for coupling together sections of sucker rods inserted into a deep well as well as to space these rods from the sides of the well.
In establishing wells for production of fluid hydrocarbon, a hole is first drilled into the ground and then logging equipment lowered into the hole and used to determine the character of the formation as a function of depth. A steel pipe or tubing, commonly referred to as casing, is then set in the bore hole down to the bottom. The casing is perforated at selected locations to allow the fluid in the formation to enter the bore hole.
In cases where the fluid is of high viscosity or where there is a relatively low pressure, it is necessary to pump the fluid out of the well. Approximately 90% of all artificial lift wells in the U.S. and Canada consist of a down hole pump connected to a surface power source by a string of sucker rods. Each sucker rod is typically 25 feet long with a diameter of 3/4" or 7/8" and is provided with a threaded pin end and shoulder at each of its ends. A cylindrical internally threaded member, typically 4" long and 15/8 inches diameter is used to couple two sucker rods together. In this way a sucker rod string is made up of a number of rods and couplings with the couplings being larger in diameter than the rods.
A sucker rod string passes through a concentric tubing string consisting of 30 foot sections of tubing having an inside diameter of 21/2 inches. Rotation or up and down reciprocating motion of the sucker rods activate the pumps depending on the type of pump employed. In rotary systems, the pump used is often a positive cavity displacement pump which consists of two mating pieces, one being stationary and the other rotating so as to create a chain of cavities moving from the bottom of the assembly to the top. Such systems have the capability to remove troublesome sand and other solids from the bore hole as well as being able to achieve high lifts at slow rotation speeds. Typical rotation speeds encountered are in the area of 600 revolutions per minute at depths of up to 4,000 feet.
Various types of couplings between sections of sucker rods are employed to centralize the sucker rod string. One common type of coupling has an exterior hard surface that turns with the rod and tends to wear out the casing. An elastomeric material is sometimes bonded to the outer surface of the coupling to reduce the wear of the casing which is more expensive and difficult to replace than is the coupling. Couplings having an elastomeric outer surface provide only a partial solution to wearing through of the casing in as much as the elastomeric surface wears away quickly and then the coupling must be replaced or be resurfaced.
U.S. Pat. No. 4,757,861 issued to Klyne discloses a sucker rod coupling assembly having a free turning vaned wheel of soft resilient material, a steel shaft with soft resilient sleeve bonded thereto and coupling end faces wtih soft resilient rings bonded to the ends thereof. The sleeve and rings prevent sand from reaching and abrading the steel surfaces of the shaft and coupling end faces. However, given that the sleeve and rings are soft and resilient, the torque transfer takes place across the stud threads rather than across the rings and sleeve to the steel shaft. Moreover, excessive wear or breaking of the wheel places the steel box end couplings in contact with the well casing or tubing resulting in wearing of the latter rather than the couplings.
A second type of coupling has a free turning vaned wheel made of an elastomer or plastic such as nylon. The wheel is designed to remain stationary and hence avoid wearing of the casing. The wheel acts as a sacrificial surface. Wearing away of the wheel moreover, simply requires replacement with a new wheel and not replacement of the entire coupling, provided that excessive wear or failure of the wheel has not occurred. Existing designs, however, because of restrictions in diameter set by the wheel, exhibit a susceptibility to breakage.
Accordingly, it is an object of the present invention to provide an improved sucker rod guide bearing.
It is a further object of the invention to provide a sucker rod guide bearing employing a free turning vaned wheel and which is capable of withstanding higher torque then other known guide bearings employing such wheels.
It is yet a further object of the invention to provide a sucker rod guide bearing with alternative sacrificial wear surfaces in the event of successive wear or failure of the free turning wheel which acts as the primary sacrificial surface.